Devices for feeding sheets having the characteristics outlined above are widely known and used in the sector art, and are employed especially on facsimile type office machines for feeding one at a time both recording sheets destined to be printed by a printing unit, and original copies destined to be read by a read unit of the facsimile system.
In these known devices the separating means are typically comprised of one or more rotating rollers, arranged adjacent to one face of the stacks and suitable for engaging with the sheet laid on the said face to pick it up off the other sheets of the stack.
One of these known devices is described in U.S. Pat. No. 4,025,066 and comprises a first tray fulcrum-mounted on a fixed structure and adapted to support a first stack of sheets, a second tray slidingly fitted on the first tray and adapted to support a second stack of sheets, and a feed roller suitable for engaging selectively with one or the other of the stacks for separating and feeding sheets from the stacks.
The second tray is adapted to selectively slide along the first tray between a forward position, wherein it completely covers the first tray and brings the second stack into engagement with the roller, and a withdrawn position, wherein it partially uncovers the first tray to grant the first stack access to the roller for a sheet to be picked up.
This device adopts highly complex mechanical solutions, requiring a particularly high number of parts to move the two trays and selectively bring the relative stacks into engagement with the feed roller. Accordingly this device may be quite expensive to manufacture as well as to maintain.